Heat transfer using a heat driver loop

ABSTRACT

A heat transfer fluid medium ( 25 ) within the closed system is arranged to boil to form a vapor in the evaporation section ( 12 ) and such that release of heat from the condensation section ( 11 ) to the fluid to be heated ( 4 A) causes the vapor to condense to liquid in the condensation section ( 11 ). The conduit forms a loop ( 10 ) and back flow in the loop ( 10 ) is prevented by providing a trap ( 27 ) of liquid in the conduit at a position adjacent to or at the evaporation section ( 12 ). The flow around the loop ( 10 ) at high speed sufficient to carry all condensate forwardly is caused solely by application of energy to the system by the heat source ( 21 ) without mechanical pumping. Inert gases are collected immediately upstream of the trap ( 27 ) and can be purged therefrom.

[0001] This invention relates to a heating system transferring heat froma heat source such as a combustion heating system to a fluid to beheated which is particularly but not exclusively designed for heatingoil in storage tanks, oil emulsion treatment tanks and oil upgrading andrefining process vessels.

BACKGROUND OF THE INVENTION

[0002] Reference is made to Canadian Patent 1,264,443 (Spehar) issuedJan. 16, 1990 and U.S. Pat. No. 5,947,111 (Neulander et al) issued Sep.7, 1999 to Hudson Products Corp (which corresponds to Canadianapplication 2,262,990) which describe prior art arrangements and thedisclosure of these prior patents is hereby incorporated by reference toshow the type of installation and use to which the present device can tobe put.

[0003] Reference is also made to the prior U.S. Pat. No. 4,393,663(Grunes) which shows a heat loop arrangement for heating variousmaterials, primarily water, within a container. However this arrangementhas not been proposed for and is not suitable for the heating of oil andparticularly crude oil in a storage tank

SUMMARY OF THE INVENTION

[0004] It is one object of the present invention to provide an improvedmethod of heat transfer from a heat source to a fluid to be heated.

[0005] According to the present invention there is provided a method fortransferring heat from a heat source to a fluid to be heated comprising:

[0006] providing a heat source;

[0007] providing a fluid to be heated at a position spaced from the heatsource;

[0008] providing a closed system including at least one conduit;

[0009] providing an evaporation section of the closed system at the heatsource;

[0010] providing a condensation section of the closed system in thefluid to be heated;

[0011] providing a heat transfer fluid medium within the closed systemhaving a temperature of boiling from liquid to vapor such that heat fromthe heat source causes the liquid to boil to form a vapor in theevaporation section and such that release of heat from the condensationsection to the fluid to be heated causes the vapor to condense to liquidin the condensation section;

[0012] the at least one conduit forming a loop extending from theevaporation section through the condensation section and back to theevaporation section so as to conduct the heat transfer fluid medium fromthe evaporation section to the condensation section and back to theevaporation section;

[0013] preventing back flow in the loop so that flow in the loop formingthe conduit can occur in one direction only by providing a trap ofliquid in the conduit at a position adjacent to or at the evaporationsection;

[0014] and causing a flow in the heat transfer medium around the loop byapplication of energy to the system by the heat source.

[0015] The trap provides a mechanism for prevention back flow which canbe designed and arranged to not only prevent back flow, , but also toutilize the adjustability of the trap to provide sufficient backpressure and force of flow to maintain flow of vapor, carry-over liquidfrom the vaporizer and condensate, substantially in one direction, anddrive this combination through resistance imposed by restrictions anddeployments, above and below the level of the vaporizer, of thecondenser.

[0016] The trap also provides a block, for any residue of the inertgases that are used for initial purging plus any inert gases that aregenerated over a period of time by chemical interaction of the fluid[s]and the materials from which the device is constructed and theaccumulation of which will progressively impair the effectiveness of thesystem, against which these gases will accumulate as swept along by thefluid flow while in operation and unable to pass through the trap, in alocation that is accessible from outside the vessel which enables thesegases to be detected and purged from the system utilizing the pressureof the system while in operation. Thus the trap is arranged so that itstops the forward flow of the inert gases at the trap and there isprovided an access opening which can be opened at the positionimmediately upstream of the trap so that the gases can be purged, withthe system under pressure so that the vapor drives out the inert gasesuntil escape of vapor is detected.

[0017] The system is primarily designed for use in heating crude oil ina tank but can also be used for other heating systems including heatingair for forced air systems and space heating. The system can also beused for heating oil in a duct of pipe as it flows past the condensationsection of the loop.

[0018] The system consists of a closed loop, sealed from atmosphere andcontaining a fluid. The fluid is vaporized in the energy absorbingsection by the application of heat. The temperature and pressure of thesystem vary in a fixed relationship according to the vaporizationcharacteristics of the fluid and the amount of heat applied. The vaporis conducted to the energy emitting section where it condenses, givingoff its latent heat. The condensate flows back through the trap to theenergy absorbing section. Vapor is driven in one rotational direction bythe liquid differential pressure of the condensate gathering trap whichself-adjusts to overcome flow resistance through the energy emittingsection of the loop. The system has no moving mechanical parts.

[0019] The system consists of a single conduit or a multiplicity of suchconduits connected by input and output manifolds to the evaporationsection at the heat source outside the storage tank or fluid to beheated.

[0020] The trap is not only self adjusting but its range ofadjustability can be increased or decreased by increasing or decreasingthe depth of the trap to permit greater liquid level differentials tooffset greater energy emitting section resistance.

[0021] The configuration of the loop and trap is such that the energy ofthe system is sufficient to both overcome the resistance of the energyemitting section but also to sustain a vapor flow velocity sufficient tocarry along with it substantially all the condensate produced in theenergy emitting section, plus a limited quantity of liquid physicallycarried out of the energy absorbing section due to boiling action. Thisis an important feature that should be designed into the configurationin order to assure the conveyance of additives, such as anti-corrosionagents and anti-freezing agents, throughout the loop rather than havethem confined to the energy absorption section due to being precipitateddue to vaporization or isolated due to selective vaporization. However,and this is important, the system should not carry over liquid from thevaporizer so as to substantially form a conventional bubble pump, suchas in a percolator, so that the degree of bubble pump action must becontrolled by the design such that it occurs only to the extentnecessary to convey the additives and not to the extent that itcontributes significantly in the conveyance of heat.

[0022] Conveyance of heat substantially totally occurs due to change ofstate at a fixed temperature rather then by loss of sensible heat fromthis liquid by a decreasing temperature of the liquid through the energyemitting section. In other words, the bubble pump action must notsignificantly interfere with the capability of the system to maintain aconstant temperature across the heating element when utilized forheating purposes.

[0023] The only portions of the system where gravity is the principalforce determining condensate flow, or liquid position, is the; trap, anytransition from the energy emitting section to the energy absorbingsection where condensate flow to the trap may be substantially directedby gravity, and, the portion of the energy absorbing section whereliquid is held in direct proximity to the heat source by theconfiguration of that portion of the system.

[0024] Consequently, the heat energy emitting section of the loop can beof any lateral or vertical deployment in relation to the energyabsorbing section, and can be of any sizing or other physicallyrestricting configuration and can accommodate whatever other loaddemands requiring pressure differential that might be placed upon thesystem, provided all of that is within the capability of the energyabsorption section to absorb sufficient heat energy and, the capabilityof the trap to withstand sufficient back pressure to overcome theresistance imposed by these.

[0025] A specific heat emission temperature can be selected by anappropriate choice of a fluid having the desired temperature/pressurerelationship and a construction capable of withstanding the pressureassociated with that temperature, and can be maintained while inoperation by controlling the amount of heat that is absorbed, bycontrolling fuel flow to the burner. The controller can be actuated bysensing either temperature or pressure of the vapor issuing from thevaporizer, which have a fixed relationship.

[0026] In practice, the system is charged with water and additives,purged with an inert gas such as argon, the internal pressure reduced toclose to a complete vacuum at normal ambient temperature, the systemsealed, and then operated at below a maximum 15 psi. This pressure rangeis readily tolerated with conventional construction and is below thepressure that would warrant classification as a pressure vessel. In someapplications, the system would then remain permanently sealed andinitial setting of internal pressure in relation to temperature and theinitial charge of fluid would remain for the service life of the device.In other applications, the system in its operational mode would besealed but provision would be made for the periodic servicing such as;removal of buildup of inert gases due to chemical interactions betweenfluid[s] and conduit material, replacement of the fluid due to chemicaldegeneration, and re-establishment of vacuum at normal ambient due toleakage.

[0027] However the system can also be operated at higher temperaturesand pressures and may use liquids different from water which may have ahigher boiling point although water is well known to provide a very highlatent heat of vaporization. The available selection of heat transferfluids is limited only by practicality, and would include for examplethose shown in the attached Table, the principle considerations andlimitations being the vaporization temperature/pressure relationshipcharacteristics of the fluids and the chemical interactivity between theheat transfer fluid and the material utilized to construct the loop. Asingle or multiplicity of heat transfer liquids can be employed in agiven system. In one arrangement, all of the transfer liquids maycirculate throughout the system in admixture by vaporization andcondensing. Alternatively, one or more of the liquids may act as a‘boiling bed’ for others depending on the temperature and pressure rangeof the system from shutdown to full operation and the vaporizationcharacteristics of the liquids. This is significant because additivesmay be required for such purposes as inhibiting chemical interaction andpreventing freezing.

[0028] Because heat transfer is substantially wholly accomplished bychange of state, the temperature of the energy emitting section isconstant throughout its length and is selectable amongst fluids havingappropriate temperature/pressure characteristics and chemicalcharacteristics. Both of these characteristics are highly desirable forprocesses that are enhanced by selectability and controllability oftemperature, such as the different processes involved in petroleumprocessing, which would include:

[0029] [a] Water and particulate matter separation from raw petroleumproduct which is facilitated by holding the raw product at as uniformand high a temperature as can be sustained below the boiling point ofwater in order to minimize viscosity which promotes separation and toavoid boiling creating foam which seriously disrupts the process due tointerference with heat transfer and other effects. It is an importantaspect of this system that not only does the uniform temperature of theheating elements contribute to maintaining a higher average temperatureof the raw product just below the boiling point of water, but, at nopoint on the element is the raw product exposed to localizedtemperatures above the boiling point of water causing localizedvaporization of water and occasioning precipitation and accumulation ofparticulate matter on the surface of the heating elements which reducestheir effectiveness for heat transfer and reduces their service life.This would be in contrast to direct fired immersion tube heaters whichfeature a large temperature differential over their length and

[0030] [b] Upgrading and refining of petroleum product, which areessentially a matter of exposure of crude product to a variety oftemperatures which are selectable, controllable, and, as constant as canbe achieved over the heat transfer surface for the purpose of producingby distillation various petroleum products which have characteristicvaporization temperatures. The effectiveness of the process, in terms ofthe purity of product, is enhanced by maintaining the crude productwithin as narrow a temperature band as possible.

[0031] Another important feature of this technology in that it is highlyadaptable to optimizing, or maximizing, heat transfer capacity inrelation to the internal volume of the system. This is of significancein relation to the regulatory requirements for pressure vessels.Pressure vessels are defined as containers in which pressure isgenerated as a consequence of applying heat, a classic example beingconventional steam boilers. There are two further stipulations to thedefinition; that the pressure generated be in excess of 15 psi, and thatthe volume of the vessel be in excess of 65 liters. Anything of lessvolume, regardless of pressure, is designated as a ‘fixture’ and is notsubject to the requirements for operating a pressure vessel. Theserequirements are onerous in that they include constant attendance by acertified person and regular inspection. Such requirements may vary inspecifics from jurisdiction to jurisdiction but will substantiallyinvolve maximum pressures and volumes.

[0032] Because the system described herein is capable of operating at agreat variety of temperatures and pressures compared to conventionalheat transfer systems involving steam or hot water due to the variety offluids that can be employed having different temperature/pressurecharacteristics, much higher heating element temperatures can begenerated than is common for steam or hot water systems and it is alsopossible to do so at lower pressures than would be produced with water.

[0033] For example, propylene glycol could be utilized which has avaporization temperature of 605 Degrees F. at 15 psi gauge pressurecompared to a vaporization temperature for water of 250 Degrees F. at 15psi gauge pressure. Thus higher temperatures, and greater heat exchange,can be achieved with propylene glycol than with water at pressures belowthe limit specified for definition as pressure vessel. Alternatively, at40 psi gauge pressure, water vaporization temperature increases to 287Degrees F. while propylene glycol vaporization temperatures rise to 1048Degrees F. Thus much higher temperatures, and much greater heat exchangecan be achieved with vessel volumes below the limit specified forclassification as a pressure vessel and therefore classified as afixture, regardless of pressure.

[0034] Hence this system provides two means of enhancing capacitywithout encroaching upon the definition of a pressure vessel, by theutilization of the higher temperatures associated with higher pressureswhile maintaining volumes below the maximum for a fixture, and theutilization of fluids that have a temperature/pressure characteristicsuch that higher temperatures can be maintained at pressures below themaximum for pressures for pressure vessels and therefore unlimited involume.

[0035] This aspect of this technology has particular significance withrespect to space and air replacement heating applications. In suchsystems, self-contained, compact heater modules incorporating highertemperature heat exchangers are an alternate to systems consisting ofconventional unit heaters, make-up air heaters, etc., incorporatinglarger, lower temperature heat exchangers, and connected to a steamboiler via a steam and condensate circulating system.

[0036] It is also significant in relation to the amount of materialemployed in relation to capacity which, in turn, relates to cost ofmanufacture.

[0037] The energy absorption section of the loop may be open to thecombustion action or may be encapsulated within an enclosed housingwhich is filled with a liquid intermediate heating medium. The use of anencapsulation and heating medium allows the heating system to sustain aneven, maximum tolerable temperature over the heat absorption surfacethus minimizing the amount of surface required and contributing to theminimization of the volume of the system pursuant. In practice, theintermediate heating medium is preferably what is referred to as athermal oil, capable of maintaining stability at temperatures close tothe crystallization temperature of mild steel. The whole heat absorptionsurface is then covered with that temperature. To the contrary, whendirectly heated with combustion products, which normally would be ofuneven temperature, only the peak temperature could be at that levelotherwise the surface would be damaged and the average would beconsiderably less. Encapsulation also enables more than one heatermodule to be supplied with heat from one central fuel combustion deviceby transferring the intermediate heating medium from that device to anynumber of heater modules.

[0038] When used for heating a process liquid within a storage tank, theheating system preferably includes an arrangement in which one or moreheating loops are heated externally of the tank and extend into the tankso that heat is transferred from the evaporation area at the heat sourceto the condensation area within the tank. The evaporation area islocated within a vessel, which may contain high temperature heating oilin an encapsulating vessel where the vessel is heated by a burner sothat the oil transfers heat to the condensation area of the single heatloop or of each loop if there is more than one.

[0039] Also, a multiplicity of condensing sections can be heated fromone vaporizer such that more than one tank or more than one space ormake-up air heater can be supplied with vapor from one vaporizationsource. The transition system from the vaporization section to thecondensation section[s] may be with rigid or flexible conduit and may besuch that the vaporizer can be located at ground or floor level withconduit conveying vapor to condenser[s] located at a higher level withinthe capability of the system to maintain fluid flow substantially in onedirection.

[0040] The burner is controlled by thermostats which may be locatedwithin the tank so that the temperature of the oil within the tank ismaintained within required limits. Alternatively, the temperature orpressure, as these are directly related, within the heat loop may bedetected for maintaining the required amount of heat input to keep thetemperature and pressure at the operating value.

[0041] An over temperature shut off is provided for safety. This may beprovided within the loop itself preferably as a pressure sensor.Preferably the shut off is of the resetting type so that combustion isre-started after a predetermined cool down period since this overcomesproblems should the over pressure situation causing the shut down tooccur be temporary. This is particularly possible where very viscousmaterials around the heat emission part of the heat loop temporarilyreduce or prevent convection currents in the process liquid in the tankcausing the emission part to overheat since the viscous materials act asan insulator. Alternatively the over temperature shut off may be locatedwithin an encapsulating heating oil so that if the heating oil exceeds apredetermined temperature the burner is shut off. Thus there is nodetection of temperature at the surface of the condensation area of theheat loop within the tank.

[0042] It is an important feature of this system that it is capable ofcycling, fairly rapidly if need be, in response to an on/offcondensation section temperature or pressure control, or, be capable ofoperating at reduced firing rates in response to a modulating condensertemperature or pressure control, during the start-up phase due to delaysin establishing full heat exchange capacity from the condenser s at fullfiring capacity because of thermal and flow characteristics of theprocess fluid being heated. Establishing generalized convectioncirculation in vessels filled with raw petroleum products can beproblematical during the heating startup phase due to high viscosities,the effect of low temperature exposure on viscosities, variations inwater content particularly as that is trapped next to heating elements,and, tendency of product to establish and accelerate flow along channelsof least resistance rather than establish overall convection currents.

[0043] Reliable, stable operation during this initial startup periodwhen demand for product temperature is at its maximum but tolerance ofheat absorption is at its minimum is a major advantage of thearrangement described herein over the Grunes et al technology whichrequires stable operation above a minimum level of heat input over aminimum period of time to establish and maintain a liquid block at the‘resistor’ in order to operate with the flow of vapor and liquid in onedirection.

[0044] The heat loop is not a heat pipe of any form and does not usesurface tension to pump the liquid back to the heated area. Instead theheat loop is a generally conduit with two generally upwardly extendinglegs and two generally transverse arms forming a loop. A trap is formedat the evaporation area at the bottom of one leg so that vapor isprevented from flowing up the leg at the evaporation area and thus thevapor is driven upwardly along the leg at the evaporation area andtransversely along the top arm from the heat source outside the tanktransversely into the body of the tank.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Embodiments of the invention are described herein in conductionwith the attached drawings as follows:

[0046]FIG. 1 is a schematic cross-sectional view of a firstconfiguration of heating system according to the present invention forthe heating of oil in tanks primarily for separation of water/oilemulsion.

[0047]FIG. 1A is a cross-sectional view along the lines A-A of FIG. 1.FIG. 2 is a schematic cross-sectional view of a second configurationaccording to the present invention.

[0048]FIG. 3 is a schematic cross-sectional view of a thirdconfiguration of heating system according to the present invention.

[0049]FIG. 4 is a top plan view of the condensation section of theheating system of FIG. 2 which is within the tank.

[0050]FIG. 5 is a schematic cross-sectional view of a configuration ofthe condensation section of the conduit for use in heating fluid withina duct.

[0051]FIG. 6 is a top plan view of a the evaporation section of theheating system of FIG. 3 which is arranged for connection to the sectionshown in FIG. 4.

[0052]FIG. 7 is a front elevational view of the evaporation section ofFIG. 6 of the heating system of FIG. 3.

[0053]FIG. 8 is a side elevational view of the evaporation section ofFIG. 6 of the heating system of FIG. 3.

[0054] Table A attached hereto shows a list of possible fluids for usein the system as heat transfer medium.

DETAILED DESCRIPTION

[0055]FIGS. 1 and 1A show a first configuration which is shown forheating a fluid within a container 4.

[0056] It will be appreciated that each of the different configurationsshown and described herein can be used in different locations forheating different materials including water, oil or petroleum productsand air. Thus in FIG. 2 the configuration is shown for use in heatingair within a duct for example in a space heating system for generatingheated air for heating a building or for example in heating make up airfor applying heat to air taken from the exterior of the building forapplying heated air into the building to make up air drawn from thebuilding in ventilation.

[0057] The configuration shown in FIG. 3 is again shown for heating orother fluid within a tank. The configuration shown in FIG. 5 is shownfor heating liquid within a pipe or duct.

[0058] However it will be appreciated that the configuration of theevaporation section as described hereinafter can vary and be selectedfrom any one of the configurations shown herein for use with thedifferent fluids to be heated. Yet further additional configurations canbe provided for the evaporation section which are not shown herein.

[0059] Advantage can be obtained by encapsulation of the evaporationsection within a heat communication medium such as a heating oil butthis is not essential to any of the configurations shown.

[0060] Advantage can be obtained by providing a manifold which connectsthe evaporation section to the condensation section so that one or moreconduit portions from the evaporation section can connect to a differentnumber of conduit portions in the condensation section. However the usefor the manifold is not essential and the system can comprise a singlecomplete conduit which communicates with both the evaporation sectionand condensation section or can comprise a multiple number of separateconduits each independently connected to the evaporation section and tothe condensation section.

[0061] Turning firstly to FIG. 1 there is shown a first configuration inwhich the fluid 4A within a tank 4 is heated by a heat loop 10 accordingto the present invention including a condensation section 11 and anevaporation section 12. The heat loop is formed by a pipe of rectangularcross section including an upper leg 13 and a lower leg 14 which areparallel and spaced by an open section 15 therebetween. The legs 13 and14 are horizontal and extend from the evaporation section outside thecontainer into the container to the condensation section 11. The heatloops pass through a bulk head 16 of the tank at one wall of the tank.

[0062] The horizontal legs 13 and 14 are connected by vertical legportions 17 and 18 which are short in comparison with the length of thelegs 13 and 14.

[0063] The evaporation section 12 is located within an encapsulatingcontainer 19 which has a cylindrical peripheral wall as best shown inFIG. 1A which fully encompasses the legs 13 and 14 and the leg portion17. It will be noted from FIG. 1A that there are provided two heat loopsside by side and it will be appreciated that the system may include onlyone such heat loop or a series of such heat loops side by side andspaced within the encapsulation container 19 and extending therefrominto the tank 4. The evaporation section is contained within a housing20 including a burner 21 which burns a suitable fuel for heating theoutside surface of the encapsulation container 19. The ends of theencapsulation container are closed by the bulkhead 16 and by an endplate 22 so as to be fully closed around the evaporation section 12 andto enclose therebetween a heating oil 23 which is heated by thecombustion from the burner 21 so as to transfer heat from the outsidesurface of the encapsulation container 19 to the evaporation section ofthe heat loops. The housing 20 includes a flue 24 for escape of thecombustion products from the burner 21 exiting from the housing 20outside the container 4.

[0064] The heat loop 10 contains a heat transfer medium 25 which is inliquid form at the bottom of the heat loop and in vapor form in the topof the heat loop. The amount of the heat transfer medium is arranged sothat the surface 26 is within the leg 14 and is confined by a bulkheadtrap member 27 at the junction between the leg 14 and the leg portion18. Thus the bulkhead trap 27 extends downwardly at the leg portion 18into the liquid below the surface 26 so as to provide a trap whichprevents vapor from entering the leg portion 18 from below thus causingvapor to flow only in the clockwise direction and around the loop andpreventing backflow of vapor.

[0065] In the evaporation section 12, the liquid is heated so as togenerate a vigorous boiling action sufficient to generate vapor rapidlyin the evaporation section. The vapor is prevented from running alongthe leg 14 by the trap 27 and thus must rise along the leg portion 17and run along the leg 13 to generate a flow around the loop in theclockwise direction. The dimensions of the loop relative to the amountof heat applied through the intermediate heating oil 23 to theevaporation section is arranged so that the vapor moves at high velocitygreater than 500 feet per minute and more preferably of the order of thespeed of sound so as to generate rapid flow of significant volume of thevapor so as to transfer the latent heat of evaporation of all of thatvolume of vapor from the evaporation section to the condensation sectionwhere all that vapor condenses. The maximum efficiency can be obtainedwhen all of the vapor is condensed and when little or no heat istransferred from the liquid to the fluid for A by cooling the liquid.

[0066] It will be noted that in the leg portion 18, there is a volume ofliquid up to a surface 26A which generates a head of liquid at a heightH which is responsive to a pressure differential across the trap 27.This pressure differential is equal to the drop in pressure caused bythe resistance to flow of the vapor within the loop from the evaporationsection to the condensation section.

[0067] In FIG. 1 is shown a control system 70 for controlling the supplyof fuel to the burner. This includes a first temperature sensor 71 inthe process liquid, generally oil, within the tank. The sensor may belocated adjacent the leg 13 and is used in conjunction with the controlsystem as a thermostat. The control system in response to the measuredtemperature acts to control the supply of fuel to maintain a requiredenergy supply to maintain a required temperature within the processliquid. A second overpressure or over temperature sensor 72 detects anupper limit pressure or temperature within the system which exceeds apredetermined operating condition. This is normally used to shut downthe system in the event that the pressure or temperature exceeds thismaximum allowable condition. When heating crude oil or similarmaterials, the process fluid at start up is often resistant to absorbingheat and thus acts in effect as an insulator surrounding thecondensation section. The control system of the present device isarranged therefore at start up to operate in response to the upper limitsensor either to modulate the fuel supply to a rate commensurate withthe rate of energy which the process liquid can absorb or to cycle thefuel supply on and off. Thus with the modulation system, the controlunit 70 is arranged to detect an over temperature condition and toreduce the fuel supply until that over temperature condition iscancelled. The fuel supply is then gradually increased until the overtemperature condition is again reached. The system then operates to finda balance at which the fuel supply is equated to the maximum heat whichcan be absorbed by the process liquid. As the process liquid increasesin temperature its resistance to absorbing heat reduces until it exceedsthe maximum energy input, in which case the maximum fuel supply ismaintained until the thermostat operates when the required operatingtemperature is reached. The on-off cycling of the fuel supply can beused in the same manner but is less efficient to increase thetemperature of the process liquid at the maximum rate since the fuelsupply rate is not optimized. Thus the temperature sensor acts with thecontrol unit as a thermostat at a predetermined set temperature of theoil and the safety over limit detector, which is responsive to an overpressure or over temperature in the conduit, is arranged to modulate orcycle the energy supplied to the evaporation section during a start upphase below the set temperature to maintain heating of the oil while theoil is resistant to absorbing heat.

[0068] Turning now to FIG. 2, there is shown an alternative arrangementwhich operates on the same principle but has a number of modifications.The evaporation section is modified so as to provide an improved heattransfer efficiency. Thus the evaporation section comprises a coil 30 ofthe loop which is shaped into a helix extending from the bottom leg 14to the top leg 13. The helical coil is mounted within a cylindricalencapsulation chamber 19A with a cylindrical heat receiving surface 19Bfacing inwardly toward the axis of the cylinder. The burner 21A islocated on the axis and comprise a simple single burner nozzle whichburns a suitable fuel primarily natural gas which thus can form anunobstructed flame within the combustion zone defined by the insidesurface 19B. Between the inside surface 19B and an outside surface ofthe cylindrical encapsulation chamber 19A is provided a heat transferoil as previously described.

[0069] The coil is spaced from the inner and outer walls of thecylindrical container leaving space for the oil to generate convectioncurrents to transfer heat efficiently and constant temperature from theinside surface to the whole of the coil housed within the cylindricalcontainer.

[0070] In this embodiment the trap within the bottom leg 14 is replacedby a U bend form of trap indicated at 27A. Thus there is formed two legs27B and 27C of sufficient length to contain the head H of the liquidwithin the leg 27C to match the pressure drop through the loop caused byresistance to flow. It will be appreciated that the resistance to flowwithin the more complex loop shown in FIG. 2 is higher than that in thesimple loop shown in FIG. 1 so that there is a requirement for anincreased height of the head H. The head is self adjusting provided thelength of the trap is sufficient so that the liquid does not pass thebottom of the trap allowing vapor to bubble over and move in theopposite or counter clockwise direction. This length can be adjusted inorder to ensure that the head H has sufficient length by increasing thelength of the U-bend. On method by which this can be achieved is byforming the section of the conduit at the U-bend from a flexible pipematerial. The U-bend can then be formed by draping the flexible materialover suitable supports arranged to provide the required leg length. Thetrap shown in FIG. 2 is outside the evaporation section separatetherefrom allowing such adjustment to be readily effected depending uponactual conditions in an installed location of the system. The vaporizersection thus may be connected to the condenser section with flexiblehose which would permit the vaporizer to be located at lower level thanthe condenser within the capability of the system to maintain desiredfluid flow characteristics. So that the vaporizer sits on the ground andcondenser tubes are at a higher level.

[0071] In FIG. 2 the upper leg includes a manifold 13A and the lower legincludes a manifold 13B allowing the manifolds to be connected to aplurality of the loops within the condensation section. Thus a singlecoil may be connected to a plurality of condensation loops or aplurality of coils may be connected to a single condensation loop or aplurality of coils may be connected to a plurality of condensationloops.

[0072] In FIG. 2, the fluid to be heated is air 4B within a duct 4Cdriven by a fan 4D. The loop 11 in the condensation section may be acomplex multi pass loop including fins 4E so as to provide a largesurface for engaging the air within the duct.

[0073] In FIG. 3 is provided an arrangement including the manifold 13Aand 13B. On the condensation side of the manifold is shown a single loopin the condensation section indicated at 11 of a simple nature. Againthe loop may be more complex including a plurality of such loops inparallel or in series. The loop in the condensation section 11 maybearranged so that the legs are horizontal as indicated in dash line 13Aor the legs may be inclined upwardly as indicated in solid line 13B. Itwill be appreciated that the inclined arrangement shown at 13B providesadditional gravitational forces for carrying the condensate back to thereturn manifold 13B. However the flow necessary to carry the medium tothe top of the loop provides an additional resistance to flow which thusmay require an increased height H of the head of the liquid within thetrap. The velocity of the flow is arranged so that the condensate withinthe first leg is carried by the vapor so that none returns to theevaporator section along the vapor leg but all is carried around at theend of the loop into the condensate leg to return to the evaporatorsection through the condensate leg and through the trap.

[0074] In the embodiment of FIG. 3 the evaporation section is defined bya pair of spaced tanks 40 and 41 which are connected by transverse heattransfer tubes 42. The arrangement of the heat transfer tubes is shownin more detail in the figures described hereinafter. The vapor leg 13 isconnected to the top of the tank 40 and receives vapor therefrom. Theleg 14 extends to the bottom of the tank 41 to form a trap 27C. Theburner 21 is located between the two tanks to apply heat to finned heattransfer tubes 42. The liquid within the tanks communicates through thetubes 32 and boils within the tubes 42 so as to generate vapor in theupper part of the tanks and the upper tubes and to generate sufficientvigorous boiling action so that the liquid also enters the upper tubesand keeps the upper tubes wetted. The vigorous boiling action generateshigh velocity vapor which enters the leg 13 and is prevented fromentering the leg 14 by the trap 27C.

[0075] In FIG. 4 is shown the manifolds 13A and 13B on the exterior ofthe tank 4. The manifolds are connected to a plurality of the loops,each including an upper leg and a lower leg 14 extending from themanifold 13A to the manifold 13B. It will be noted that in FIG. 4 thebottom leg 14 is offset to one side of the top leg 13 so that the leg 13does not lie directly vertically above the leg 14 but instead both areexposed in plan view. This arrangement maybe provided in order to allowincreased communication of heat by convection in the vertical directionfrom the upper surfaces of the legs 13 and 14.

[0076] Turning now to FIGS. 6, 7 and 8, there is shown more detail ofthe configuration of evaporator section shown in FIG. 3. Thus the tanks40 and 41 shown in plan view in FIG. 6 are connected to the pipes 13 and14 which extend to a connector plate 43 and 44 respectively forconnection to an additional duct portion extending from the connectorplate to the respective manifold 13A, 13B. The tubes Interconnecting thetanks 40 and 41 are arranged in two rows 42A and 42B with the row 42Aarranged between the tubes of the row 42B so as to allow heat andcombustion products passing between the tubes of the row 42B to impactupon the underside of the tubes of the row 42A. This configurationimproves the communication of heat from the burners 21 underneath thetubes to the tubes and to the liquid boiling within the tubes. A fluevent is communicated with the chamber 45 surrounding the tubes on thecombustion zone and extends from the top of the combustion zonerearwardly and then upwardly to a top connection plate 47 of the flue46. The legs 13 and 14 include horizontal portions extending rearwardlytogether with vertical portions which extend downwardly into the top ofthe respective tank at a position midway across the width of the tank.The combustion chamber is mounted on a stand 50 which is located undersuitable frame members 51 of the structure which support the combustionchamber.

[0077] In FIG. 5 is shown a concentric arrangement which is provided asa condensation section from the leg 13 to the leg 14 where thecondensation section is formed as a hollow cylinder within a duct 60.Fluid flowing within the duct thus enters a wider section of the duct asindicated at 60A within which is located the hollow cylinder 61 formingthe condensation section. Thus the fluid within the wider section 60Acan pass around the outside of the hollow cylinder and also through aninterior 62 of the hollow cylinder to provide an increased contactsurface between the condensation section and the fluid to provide animproved heat transfer therebetween as the medium condenses within thecondensation section.

[0078] The condenser heat exchanger which is a hollow section metal mayhave a single vaporizing section or may lead to one or a multiplicity ofcondensing sections.

[0079] The vaporizer water legs are fabricated metal containers formingmanifolds for the condenser heat exchanger sections.

[0080] The vaporizer heat exchanger is a hollows section metal which maybe finned and can be increased or decreased in number and length inorder to increase or decrease efficiency of heat exchange from heatingsource.

[0081] The heating medium may be any liquid or liquid mix, typicallywater or water/glycol, generally including a metal passivating agent.

[0082] The heat source may be a direct flame from an introduced flame,or could also be heated via a secondary heating medium such as hot oildelivered to an encasement around the vaporizer heat exchanger tubes. Acommon source of hot oil can heat either a single or a multiplicity ofHeat Driven Loops.

[0083] The pressure differential trap may be a condenser return legextended down into the condensate tank.

[0084] The liquid level differential and pressure creates pressure thatimpels vapor into outlet leg of condenser and prevents back-flow ofvapor into return leg.

[0085] Vapor flow, that is the velocity of vapor, as dictated by thecross sectional area of the outlet leg, the resistance to flow of thecondenser, and the pressure differential across the outlet and returnlegs of the condenser created by the liquid level differential in thetrap, carries all condensate in the direction of vapor flow.

[0086] Condensate flow, that is the condensate driven back to thevaporizer is effected by vapor flow but there may be some gravityassistance if condenser operating angle is above horizontal.

[0087] This allows a range of condenser operating angles fromhorizontal. The. above principle is expected to be effective in movingthe major flow of condensate in the same direction as the vapor atangles of at least 10 degrees from horizontal. ‘Effective’ can bedefined as substantially achieving the enhancement of heat exchangeassociated with uni-directional flow of vapor and condensate as opposedto counter-directional flow. Theoretically, by increasing the trapdifferential pressure and regulating the size of the outlet leg of thecondenser, the angle from horizontal could be extended to 90 deg.

[0088] There is a region of turbulent boiling in the sealed system andthe starting pressure can be regulated to anything that can be achievedabove a complete vacuum. Having established the starting pressure, thevoid space is generally purged with an inert gas, such as argon.Especially under vacuum conditions, boiling will be turbulent with largebubbles of steam carrying globs of liquid along with it, but without theliquid bridging the conduit to avoid the formation of a bubble pump.These globules of water will splash Into the upper vaporizer heatexchanger tubes keeping them wet, and, to some extent, be carried intoand possibly through the condenser.

[0089] It is the adjustability of the differential pressure between thesupply and return legs of the condenser plus the ability to achievehigher pressures sufficient to overcome resistance imposed by morecomplex configurations, even involving the entraining and lifting ofcondensate, that distinguishes the arrangement of FIG. 3 from thearrangement of FIG. 1 of the technology. The arrangement of FIG. 1 hasits particular merits in that it has a very simple layout that does notrigidly confine the heating medium in any part of it. Therefore themedium can be water only, which can freeze without the accompanyingexpansion damaging the device, and that the device can be fired withoutharmful effects from a frozen condition. Utilizing water only canpresent an advantage in that exposure to heat can cause breakdown ofchemically more complex substances [such as glycol]. In the oilindustry, these devices will commonly be used outdoors, so thesequalities could be of significance.

[0090] Other load demands could consist of mechanical utilization ofenergy. This would include, for example, the driving of a turbine forany number of purposes including the generation of electricity, thedirect driving of a pump, fan, etc.

[0091] It may be possible to utilize mechanical back-flow resistingdevices such as ball-check, swing-check, or, spring-loaded valves suchas to increase resistance to back pressure. However in practice,mechanical methods of blocking back pressure may be impractical in thatthey eventually will require maintenance. Conventional steam traps, forexample, are susceptible to occasional problems. Compared toconventional steam systems, the present invention may use differentliquids, higher temperatures, higher vapor and condensate velocitiesetc, plus a need for rugged reliability. It is one of the distinguishingfeatures of the present arrangement that it is entirely ‘thermodynamic’,i.e., heat driven, without any moving parts.

[0092] One problem which can arise is the accumulation of inert gaseswhich is a commonly encountered phenomenon with this type of technology.A gradual build-up of inert gases occurs in these systems, depending onmaterials utilized and chemical action between them, which displacesvapor and decreases effectiveness, which, with single tube technology,sometimes determines service life because its effects are not readilymonitored or remedied. It is inherent to the present principal ofoperation that this major concern becomes much more manageable and istherefore an important feature of the invention.

[0093] A loop with significant force of flow such as the presentarrangement, has the advantage that any inert gases in the system willbe driven into what Is referred to as an accumulation sector, which isthe sector of the loop just before the trap and will be confined therewhile the system is in operation due to the forward flow of the vaporand the locking or trap effect of the liquid in the trap. Thus an accessopening 75 is located immediately in advance of the trap for sampling ofthe presence of inert gases and for purging of those gases. It will beappreciated that in the presence of such gases, the opening of theaccess opening by service personnel will cause the vapor pressure andflow to discharge the inert gases through the opening until the presenceof vapor in the discharge indicates that all gases have been purged.Such inert gases may be introduced for purging and subsequently notfully evacuated, such as argon which is commonly used for this purpose,and/or produced as a result of chemical activity such as hydrogen asfrom reaction between water and iron, the predominant element in mildsteels and present to some degree in stainless steels, and which occurseven in the absence of free oxygen, hence the need for passivatingagents. With the arrangement as described herein, that sector wouldnormally be out of or at least extending partly out of the immersedportion of the heating element, the significance being that it isaccessible in that it will not be completely Immersed. The build up ofinert gases can be detected by a decrease in temperature in an area ofthe conduit immediately upstream of the trap which is caused by theinert gases preventing the vapor from condensing in that area and thusproperly heating the conduit. Thus the temperature at this area can bemonitored on an ongoing or periodic basis to detect an unacceptablebuild up of the inert gases. Alternatively, the inert gases when theybuild up will reduce the vacuum in the system when shut down and againtheir presence can be detected by service personnel carrying out apressure test at shut down and detecting the presence or reduction ofthe initial preset vacuum level.

[0094] With single tube technologies whether tubes are employed singlyor in a plurality, such as conventional heat pipes and thermo-siphons,as in the prior art of Spehar and Neulander mentioned above, and whichare commonly employed sloped upwards into the vessel, the inert gasesaccumulate and remain, whether the system is in or out of operation, inwhat is referred to as a ‘block’ in the high end of the tube, which isthe sector furthest immersed in the process fluid and most inaccessible.

[0095] In a sector where there is such accumulation of inert gases, heatexchange is significantly impaired because the inert gases block outvapor and preclude the change of state which is the substantial means ofconveying heat. Only sensible heat from liquids that may flow throughthe sector would be transmitted from the accumulation sector.

[0096] With loops, the decline is such that effective heat exchange issignificantly impaired but not altogether eliminated because there is atleast some sensible heat available from condensate and throw-over liquidflowing through that sector. At the boundary between the sector of theheating element that is performing normally and maintaining asubstantially constant temperature, and the sector where there isaccumulation of inert gases, heating element temperatures start todecline in an observable, significant, and regular fashion.

[0097] However, with single tubes, there is no such flow of liquid andheating element temperatures will decline much more drastically and thatsector is effectively ‘blocked’, or idled, for heat exchange purposes.Moreover, with loops, when in full operation and the system underpositive pressure, the accumulation is moved to a sector that isnormally accessible for measurement of temperature, the differencebetween the entry temperature of vapor to the heating element and thetemperature in the accumulation sector being an indication of the degreeof accumulation of inert gases, and purging of the inert gases,utilizing the operating pressure of the system itself, usually from thehighest point in the system just prior to the trap.

[0098] There Is no practically convenient means of either measuring, oreven detecting, such accumulation with single tubes, which occurs at itsgreatest extension into the process fluid, and similarly, no practicallyconvenient means of purging such accumulation if it could be detected.With single tubes, such measurement and purging devices would have toextend back through the tubes themselves or through the vessel. Theseare very difficult environments warranting correspondingly expensivesolutions compared to the simple access provided by the present system.

[0099] This a significant improvement presented by the present systemover all single tube technologies also over the prior art of the Gruneset al technology when operating below that critical level where it flipsfrom unidirectional flow, which causes such accumulation to occur in asector next to the trap as above, to counter-directional flow which,with its particular configuration, would likely cause dispersion of theinert gases throughout the system while in operation which wouldgenerally impair effectiveness, and, accumulation at a highest pointwhen not in operation.

[0100] The heating of water and petroleum products, especially crudepetroleum products that are towards the ‘heavy’, that is comparativelyviscous end of the scale, present differing problems. Water iscomparatively easy to heat. Resistance to heat transfer is at itsminimum at commencement when temperature differential is at its greatestand increases as temperature rises. Convection currents are readilyestablished and the whole process is quite dependable and predictable.For heating purposes, water properties are ‘constant’, on both a case tocase basis, and with respect to any individual case. With petroleum, onthe other hand, heating properties are much more variable and complex inthat:

[0101] [a] Petroleum has ‘non-Newtonian’ flow characteristics. This hasto do with viscosity varying not only with temperature but with alsoflow velocity and boundary effects between currents in differentdirections in the same vessel. In other words, flow, particularlyconvection flow, tends to be affected in rather unpredictable ways byspecific configurations of vessels and heating elements. This effecttends to be more pronounced with heavier, more viscous, petroleumproducts.

[0102] [b] Crude petroleum product varies greatly in content andcharacteristics; viscosity of liquid petroleum product, proportion ofliquid petroleum product, amount of entrained gaseous petroleum product,proportion of water, salinity of water, amount of entrained particulatematter, sand, usually and associated more with heavier product, thesewould be the main variables.

[0103] [c] Boundary effects between the heating elements and petroleumproducts are much more problematic, with crude petroleum especially, inthat; resistance to heat transfer will always be higher than with waterand will be variable depending on the effects of all of the forgoing,and, the flashing of petroleum products and/or entrained water intogases causes foam to collect in the immediate vicinity of heatingelements which further resists heat transfer.

[0104] [d] Also, petroleum products, particular heavier crude products,have a tendency to ‘channel’, at least initially, when being heated,i.e., set up localized convection currents which get hotter, lessviscous, and therefore more active, while bypassing volumes ofun-circulating and unheated liquid. Eventually, enough heat istransmitted to these un-circulating volumes that they become entrainedin an overall convection flow pattern.

[0105] [e] The foregoing are ‘non-constant’, as well as variable, in thesense that same configurations do not always set up same flow patternsand rates of-heat transfer, as is the case with water, because thesummation of the effects of the foregoing always produce some netdifferences with respect to flow and heat transfer characteristics andthese differences are often not of an observable nature and scale.

[0106] With water, the heat loop system may have a heat transfer rate of10,000 btuh/sq.ft. of heat exchange surface at commencement of heatingat somewhere just above freezing which will decrease in a regularfashion to perhaps 8,000 btuh/sqft when the water reaches a controltemperature of somewhere just below boiling. With a vessel of a givensize and configuration, filled to a given level, and heated with aheater of a given size, configuration and capacity, this type of resultwill not vary from instance to instance.

[0107] With petroleum product, at commencement of heating with cold,stiff and highly adulterated product, the initial heat transfer might bevery low, say in the order of 200 btuh/sq.ft. of heat exchange surface.This may rise to 1000 btuh/sqft as convection circulation is establishedand then decrease to 800 btuh/sqft as control temperature is reached. Aspreviously indicated, this may vary from instance to instance, even in agiven application.

[0108] The differences between the heat transfer characteristics ofwater and petroleum products tends to be amplified with; cruder, asopposed to more refined, and, heavier, as opposed to lighter, petroleumproducts.

[0109] In other words, the technology must cope not only with greatvariation in demand, but great variation in heat transfercharacteristics as load is imposed. It is inherent to the present designthat it will self-adjust to all of his—there will be unidirectional flowfrom startup to shutdown, and at all levels, of operation.

[0110] That is not the case with the Grunes et al technology. Heatingpotable water is an application that lends itself readily to fullon/full off operation. It is inherent to the Grunes et al technologythat it will tend to flip back and forth between two modes of operationat intermediate levels of operation. It must get up to some minimumlevel of operation to either; flip over through boiling action, orcreate through condensation, enough liquid to maintain a level in theaccumulator, which is critical to establishing and maintainingunidirectional flow. At below that level of operation, the restrictionand the accumulator associated with it, which has a largely fixed, atleast a minimum, draining rate, will remain clear of liquid. Vapor andcondensate will flow in opposite directions in both legs of the devicein the manner of a conventional, single tube thermo-siphon. It couldactually be considered to be two single tube thermo-siphons abuttingeach other at both ends.

[0111] The arrangement of the present invention has an improvedoperation because:

[0112] [a] the amount of material employed in relation to the amount ofheat transferred. Because transfer is being accomplished by change ofstate, the amount of energy that can be transferred by a given amount offluid is proportionate to the rate at which the fluid is circulated eachcycle representing the transfer of the total latent heat capacity of theamount of fluid in the system. By maximizing flow rate and thereforeheat transfer rate both the amount of fluid required and the amount ofmaterial required to create the necessary volume to contain it will beminimized. That would be within the physical capability of the system totransfer heat in and out, of course, but that too can be enhanced inrelation to volume enclosed by the addition of suitable fins tofacilitate heat transfer, encapsulation to maximize average contacttemperature, etc. Maintaining flow rate of vapor and condensate in onedirection, as compared to vapor in one direction and condensate in theother and resisting each other, at all levels of operation, willmaximize effectiveness. The capability of accomplishing and maintainingthat at all levels of operation in this particular applicationrepresents a considerable improvement.

[0113] [b] the ability of the device to sustain a driving force throughthe system at all levels of operation. This extends beyond [a] above inthat there are potential applications where the ability to createpressure differentials and overcome resistance is a critical to thedevices operation. This would include any application where the systemis utilized to perform a mechanical function. With the Grunes et altechnology, at below some critical level of operation, such a devicewould cease to operate.

[0114] Points [a] and [b] in particular are general advantages that thepresent technology presents over the Grunes et al technology. Thecapability of maintaining stable operation under varying andunpredictable loading, a common condition in some aspects of petroleumprocessing, particularly with cruder and heavier products, is a specificadvantage in that application but presents potential advantages in otherapplications as well. Point [b] above is not directly associated withthe heating or processing of any particular substance it is simply anadvantage to have a device that provides a force to operate something tobe capable of doing so throughout a full range of operating levels asopposed to just an upper portion of that range.

[0115] There are a number of different types of traps which are possiblefor use with this construction;

[0116] 1. A submerged bulkhead which is shown in FIG. 1. With thisconfiguration, the liquid must flow under a bulkhead to pass into thevaporizing area. The down-leg of the trap is made distinct from thevaporizing area by this panel but the up-leg of the trap and thevaporizing area are one and the same.

[0117] 2. The “U” Trap shown in FIG. 2. The legs of the trap areseparated by being placed in separate vertical conduits joined at thebottom with the up-leg of the trap leading into the bottom of, and isdistinct from, the vaporizing area.

[0118] 3. The Down-leg Trap shown in FIG. 3. In this configuration, theup-leg of the trap and the vaporizing area are one and the same.

[0119] All these work according to the same principle—back pressure inthe vaporization area opposed and balanced by liquid level differentialpressure in the trap. The range of back pressure that can be toleratedcan be adjusted in all three cases by increasing the depth of the trap.

[0120] The “U” Trap configuration presents the advantages;

[0121] It is a simple and straightforward matter involving minimaladditional material to increase its pressure range by making the “U”deeper, whereas increasing the range of the other configurations wouldinvolve deepening the whole vaporization area, which would involveconsiderably more bulk, and, it is inherent to the “U” Tube approachthat violent boiling action will not penetrate through to the up-legbecause the up-leg will always be in its entirety below the boilingarea, which is not necessarily the case with the other twoconfigurations. It could be claimed that these configurations are moresusceptible to violent boiling action reaching the up-leg of the trapwhich would then nullify or substantially impair the desired effect ofdriving flow in one direction.

[0122] However, having said all that, it is a simple matter to adjustthe other configurations to these disadvantages simply by having thebulkhead and the open-ended conduit descend into a well provided forthat purpose in the bottom of the vaporization area.

[0123] The submerged bulkhead and the Down-leg traps have an advantageover the “U” Trap in that extra material is not required for the up-leg.

[0124] The down leg trap shown in FIG. 2 has the advantage that thecondensate is collected in the heating source and hence remains heatedwithout losing any heat by sitting in a separate or exposed trap. Thiscould be overcome by providing suitable insulation.

1. A method for transferring heat from a heat source to a fluid to beheated comprising: providing a heat source; providing a fluid to beheated at a position spaced from the heat source; providing a closedsystem including at least one conduit; providing an evaporation sectionof the closed system at the heat source; providing a condensationsection of the closed system in the fluid to be heated; providing a heattransfer fluid medium within the closed system having a temperature ofboiling from liquid to vapor such that heat from the heat source causesthe liquid to boil to form a vapor in the evaporation section and suchthat release of heat from the condensation section to the fluid to beheated causes the vapor to condense to liquid in the condensationsection; the at least one conduit forming a loop extending from theevaporation section through the condensation section and back to theevaporation section so as to conduct the heat transfer fluid medium fromthe evaporation section to the condensation section and back to theevaporation section; preventing back flow in the loop so that flow inthe loop forming the conduit can occur in one direction only byproviding a trap of liquid in the conduit at a position adjacent to orat the evaporation section; and causing a flow in the heat transfermedium around the loop by application of energy to the system by theheat source.
 2. The method any preceding claim wherein the flow of theheat transfer medium around the loop is effected in response to thechanges in state of the heat transfer medium.
 3. The method anypreceding claim wherein the flow of the heat transfer medium around theloop is caused by energy supplied substantially solely by the heatsource.
 4. The method any preceding claim wherein the flow of the heattransfer medium around the loop is caused without assistance frommechanical propulsion of the medium.
 5. The method any preceding claimwherein the liquid trap provides a column of liquid defining a pressuregreater than a pressure drop in the vapor caused by resistance to flowof the vapor in the conduit.
 6. The method according to claim 5 whereinthe liquid trap is defined by a leg in the conduit having a lengthgreater than the required column of liquid so as to allowself-adjustment of the column within the leg.
 7. The method according toclaim 6 wherein the length of the leg in the conduit is adjustable andis adjusted to provide a length matched to the required pressure drop.8. The method according to claim 7 wherein the portion of the conduit atthe leg is formed of a flexible pipe allowing the length of the leg tobe adjusted by moving the portion.
 9. The method any preceding claimwherein at least part of the condensation section is raised above theevaporation section such that condensate can flow under gravity back tothe evaporation section.
 10. The method any preceding claim wherein theflow of vapor from the evaporation section to the condensation sectionis at sufficient velocity to carry all condensate forwardly to aposition where it can flow around the loop under gravity back to theevaporation section.
 11. The method any preceding claim whereinsubstantially all the vapor generated in the evaporation section iscaused to condense in the condensation section.
 12. The method anypreceding claim wherein substantially no heat transferred is transferredto the fluid to be heated by cooling of the condensed liquid.
 13. Themethod any preceding claim wherein the conduit is arranged relative tothe evaporation section such that boiling of the liquid in theevaporation section causes non-vapor additives in the liquid in theevaporation section to be carried into the conduit with the vapor. 14.The method any preceding claim wherein the conduit is arranged relativeto the evaporation section such that boiling of the liquid in theevaporation section does not cause liquid to bridge the conduit so as toact as a bubble pump.
 15. The method any preceding claim wherein theconduit is arranged relative to the evaporation section such that thevelocity of the vapor is greater than 500 ft/sec.
 16. The method anypreceding claim wherein the pressure in the system is less than 15 psiabove atmospheric pressure.
 17. The method any preceding claim 6 whereinthe system is evacuated prior to start up.
 18. The method any precedingclaim wherein the vapor flow and the trap are arranged such that inertgases collecting in the system are driven to a location immediatelyupstream of the trap.
 19. The method any preceding claim 8 wherein thereis provided a discharge opening immediately upstream of the trap whichis opened to cause purging of collected inert gases.
 20. The method anypreceding claim wherein the evaporation section comprises a containerfor the liquid with the conduit connected to the top of the container toreceive vapor therefrom.
 21. The method any preceding claim whereinthere is provided an intermediate heating oil to transfer heat from theheat source to the evaporation section so as to allow protection of thestructure of the conduit both at high temperatures against heat damageand at low temperatures against corrosion from condensate.
 22. Themethod according to claim 21 wherein the heat transfer oil is located ina cylindrical body defining a cylindrical interior wall and acylindrical exterior wall with the evaporation section therebetween inthe form of a helical coil and with a burner inside the interior wallproviding combustion in a chamber defined by the interior wall.
 23. Amethod of heating oil in a storage tank comprising: locating the oilwithin a storage tank; providing a heat source outside the storage tank;providing at least one elongate conduit within the storage tank in theform of a loop extending from an inlet across the tank and returning toan outlet; and transferring heat from the heat source to the oil in thetank by a method any preceding claim.
 24. A method of separating anemulsion of crude oil and water in a storage tank comprising; locatingthe oil within a storage tank; providing a heat source outside thestorage tank; providing at least one elongate conduit within the storagetank in the form of a loop extending from an inlet across the tank andreturning to an outlet; and separating the oil and water into layerswithin the tank by transferring heat from the heat source to the oil inthe tank; wherein the heat is transferred by a method any precedingclaim.
 25. The method according to claim 24 wherein there is provided aplurality of conduits in the tank each connected to an inlet manifoldand to an outlet manifold.
 26. The method according to claim 24 whereinthere is provided a temperature sensor for acting with a control unit asa thermostat at a predetermined set temperature of the oil and whereinthere is provided a safety over limit detector responsive to an overpressure or over temperature in the conduit and which is arranged tomodulate or cycle the energy supplied to the evaporation section duringa start up phase below the set temperature to maintain heating of theoil while the oil is resistant to absorbing heat.